System of motor control for hoists



July 31, 19345 J. F. SCHNABEL 1,968,174

SYSTEM OF MOTOR CONTROL FOR HOISTS Original Filed Aug. 4. 1930 F/ci. 3,

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A TTORNEY.;

Patented July 3i, 1934 UNITED STATES 1.06am SYSTEM or moron coN'raor. son. aors'rs Jamel F. Schnabel, Gleveland, Ohio Application August 4, 1930, Serial Renewed February 4.

No. 472.1 1933 l s calm. `(ci. 11s-' url The present invention relates to a system of control for the operation of electric motors, and` more particularly where the motor is used on hoisting apparatus both for raising the load and for lowering the same, and the system is more particularly adaptable for the controlling of the lowering movement particularly to obtain a satisfsctoryl dynamic braking control.

The object of the present invention is to provide a control system in which all of the resistors are in use in the circuit during the entire lowering movement, and also to use the resistors assembled in as few banks as possible. Thev importance of such an arrangement is clear, when it is understood that the object of dynamic braking control in lowering is to provide for the dissipation of the potential energy stored in the load by allowing the motor to act as a generator when driven by the descending load. This energy which is released is then radiated in the form of heat from the resistors suitably placed in the control circuit. It is possible to returnla part of the energy to the power line, but the larger part must be dissipated from the resistors and it is very' desirable, therefore, to make use of all the resistors during lowering movement so as to obtain the greatest amount of heat dissipating material, and thus in turn reducing the weight and cost of the control mechanism.

This arrangement is also desirable because o many hoists, the empty hook or light loads that will not overhaul, must also be lowered and although the potential energy under these conditions is not suiilcient to overcome the friction of the mechanism, the resistors are required to dissipate a considerable amount of energy even under this condition. The hoisting motors are commonly made with series fields but, in 10W- ering, the eld is normally connected across the line similar to a shunt wound motor.

Most of the resistors are placed in the circuit in such a way that they will limit the current that can ilow in the series ileld from the power line if the load that is being handled is not suillciently heavy to furnish the energy to magnetize the field so that even under light load conditions, a very considerable amount ofy energy in the form of heat must be dissipated from the resistors. In such a control system for hoists, there must also be provided a conslderablerange to draw considerable energy from the line in order to produce a strong field inthe motor and at the same time it is necessary to reduce the line voltage as applied to the armature to a low value. This makes it necessary for the resistors to radiate a larger amount of energy at low lowering speeds for light loads as well as heavy loads.

Heretofore dynamic braking controllers have hada part of the resistors short-circuited or left out of the circuit on the ilrst few points in lowering and provision has been made for inserting such resistors in the field circuit as the controller is moved to the full speed lowering position. This type of control gives a strong field yfor the low speeds and a weaker field for the higher speeds. In some control systems additional resistor banks have been used for reducing the voltage onboth the field and amature on the first few lowering points, and these resistors have then been cut out and remain unused on the remaining points of the controller. In the present controller, the system is so arranged that all of the resistors are inthe circuit during the entire lowering operation.

On lother systems of dynamic braking, ilxed resistances are used in the armature. path in lowering and such -resistances are usually of rather high value to insure the release of the magnetic brake as a too rapid increase of the resistors in the eld and brake path, obtained by rapidly moving the controllerbefore gravity can accelerate the load, will allow the most oi the current to flow through the armature path and reduce' the flow through the ileld and brake circuit so low as to prevent the brake being entirely released. A high iixed resistance in the armature path on the last few points will also reduce the voltage on the armature when lowering light loads and make its speed slower than is desired and at the same time such type of fixed resistance will increase the speeds of overhauling loads unduly. In the present system the resistan of the two parallel paths may be maintained at such relative values es will give proper operation of the brake and the necessary torque to start the motor, until the last few points of the controller, when the resistance remaining` in the armature path may be reduced to a minimum. Such a system makes the controller better adapted for use with brakes of varying operating characteristics and improves the lowering speeds which can be obtained and makes it possible to obtain high speeds with the light loads and to obtain close control ofthe slower speeds for the lheavy loads. To the-accomplishment of the foregoing and related "ends, said invention, then, consists of the means hereinafter fully described and particulal'ly pointed out in the claims. y

The annexed drawing and the following description set forth in detail certain mechanism embodying the invention, such disclosed means constituting, however, but one of various mecihanical forms in which the principle oi the invention may be used.

In said annexed drawing:

Fig. 1 is a diagrammatic wiring circuit showing the controller for the lowering direction at the first lowering point; Fig. 2 shows the safety dynamic braking circuit at the oil-point; Fig. 3 is a wiring diagram showing the hoisting circuit; and Fig. 4 is a wiring diagram of a. drum-like controller arranged to obtain the circuit shown in Figs. 1, 2 and V3.

In Fig. 1 there is illustrated a motor having an armature 20 and a field coil 21 and a brake coil 22 in series with the eld, two resistor banks A and F and the two-line wires, L1 and L2, the line L1 being connected to the motor circuit between the armature and ileld, the other line L2 being connected to a point between the two resistor banks. One end of resistor bank A is connected to one end of the armature and one end of the resistor bank F is connected to the brake coil, the other ends of the two resistor banks being connected together in the lowering position by the connection S. The controller also provides a movable bridge 25, which in the position shown, is connected across between the two resistance banks. In Fig. 1 the first control point of the lowering position of the controller is shown, and in this rst point as indicated, the resistor bank F is connected in series with the iield and brake coils 21 and 22, while the resistor bank A is connected in series with the armature 20, the line wire L1 being connected between the held and armature to form parallel circuits, and the line wire L2 being connected to the circuit beyond the outer ends of the resistor banks A and F, this circuit with the connection S closing the paths from the other ends of the resistor banks.

As the controller is moved toward the full lowering speed position, the bridge moves toward the right as shown in the diagram until yit reaches the ends of the resistor banks, and thus both banks of resistors are maintained in parallel circuit during the movement of the controller over the contacts.

The L2 side of the line is also a movable contact and this contact moves to the lett as the bridge 25 moves to the right, but is maintained beyond the end of the bank A until the bridge has reached the ends of the banks of resistors. After the bridge has reached the ends of the resistor banks, the contact for L2 is moved over the contacts on resistor bank A until it reaches the last point as shown in dotted lines in Fig. 1. The bridge connection 25 during this latter movement of L2 may be maintained across the ends of the two resistor banks or may be moved clear of the bank contacts, the parallel circuit between the banks then being maintained by the connectionS.

Assuming that4 the current flows from the power line L1, the current from the line will divide and will ilowy in one path through the ileld 'and the brake and also in the parallel path through the arnaature and out through line L2. The current which ilowa ln the path through the iield and lbrake will be limited by the resistor bank F and the current iiowing in the armature y path will, at the time of starting, be limited by the resistor bank A. If the load is not heavy enough to overhaul the motor, the current will continue to now in the armature circuit, but ii.' it overhauls, the motor will then act as a generator and current will flow in the opposite direction in the armature path. The speeds o! the overhauling loads will be limited by the circuit of lesser resistance formed by the bridge, but on loads that will not overhaul, the bridge has less eiect. This bridge may be so connected on the various points as to maintain at all times the desired balancing of the held and the armature paths in order to insure enough current in the ileld path to obtain prompt brake release and also to obtain sumcient current in the armature path to provide the' necessary motor torque.

Ihe bridge 25 also provides at the rst point a dynamic braking circuit, that is, the closed circuit around and including the armature, iield and brake and as shown, one division of resistor bank ,A is included in this dynamic braking circuit.

'I'he location oi' the ends ot the bridge on the two banks A and F will be at such points as to maintain the desired relative resistance values of these two banks to suit the conditionsunder which the motor and the brake are operating and to obtain the necessary speeds. The speeds of overhaullng 'loads will increase as the controller is moved toward the full speed lowering position as more resistance is introduced into the local dynamic braking circuit which is formed by the movable bridge connection.

- Speeds of loads which will not overhaul will also increase, though not as fast. This is due to the increase in the voltage applied in the armature and the increase in the resistance shunted around the armature. On the nal points of the controller, the held magnetism will be weakened by the insertion of a part of or all of bank A in the field path and the voltage on the armature will be increased to nearly full line voltage since only a very small part of bank A is left in series with the armature across theline. 'I'his gives a larger increase in speeds for the light loads, but

for heavy loads, the increase in speed will not bey so-great as the resistance of the local dynamic braking circuit is maintained at the same value as on the preceding points.

I! failure of power should occur during the lowering, the motor would stop unless theA load is so heavy as to overhaul suiliciently to furnish the necessary energy for keeping the brake re-- bringing the controller to the of! position. The

back electro-motive torce of the motor is in the proper direction to maintain the ileld excitation.

At the of! point of the controller as shown in Fig. 2, the power line is disconnected, but the dynamic braking circuit through the motor is maintained, butthe brake coil 22 is now left out of the circuit so that the brake will set and hold the hoist and load in its position. It will be seen that at this oil-point, the dynamic braking circuitassists the magnetic or friction brake to bring the load to rest from the slow speed at the ilrst -point and thus reduces the wear on the brake to a minimum. A

In Fig. 3 the armature 20 is shunted by means of a connection 26 on the rst point with one division of bank A, the remainder being in series with the armature. On the second point the connection 26 from the end of a bank A to a point between the armature and the field remains the same, but the contacting connection for L1 il moved to the right to the second step and thus two divisions of resistor bank A are shunted around the armature with the remaining two in series. It is not desirable to use all of the resistors of banks A and F in series with the motor on the first point in hoisting as the current ilow would not be enough to operate the series brake or to give suflicient torque to keep the heavier loads from going down when they should hoist. That part of the resistor bank A which is not desirable in the motor circuit, can either be left out during hoisting, or it may be used for the armature shunt as desired.

' This system of control may be used or obtained from controllers o i.' various types,'but the controller indicated as shown in Fig. 4 is a drum type controller which may be as satisfactorily employed as either-a face plate type of controller, or con- V troller of the magnetic contacter type.

'fingers will be connected together to give the desired circuits through the armature, field, brake and resistors on the various points of the controller. Fig. 4 shows a development of the surface of this drum and to understand the operation, it is only necessary to consider the movement of the entire plane of contacts to the right t or left of the position shown, that to the rightI being the hoisting sde which brings into engagement with the stationary contact fingers A the movable hoist contacts, while movement to the left brings into engagement with the contact fingers the movable lowering contact segments. The vertical lines marked 1 to 8 inclusive on each side represent the points of various speeds for both lowering and. hoisting line 1 in each case giving the lowest speed for each direction and the lines 8 giving the highest speed for each direction with gradual increases in speeds on the intervening points. Certain of the contacts C on the cylinder are joined together in groups. The drawing shows connections by full lines between the rectangular spaces or contact segments which -represent the contacts proper and the groups are numbered as will be hereinafter explained to show the operating conditions.

As illustrated, five stationary contact fingers A and 3DF are connected to each bank of resistors to obtain four divisions ineach bank. but

a greater or lesser number of divisions may be used depending upon the controller and motor size and the use to which it will be put.

With the controller on the hoist side, current will flow from L1 through wire 40, blowout 3l and wire 41 to the contact nger 42A engaging one of the contacts 3A of group 3, through the connected contacts 3b-c--d-e toy one of the contacts 30A; on the first point the current enters the bank at the second contact from the bottom and passes through all, exceptthe end divison of the resistors to the armature..v On succeeding steps, the currenthenters bank A through contacts 3b-c-d, leaving additional divisions of the resistor bank A out of the circuit until on the cuit.

hat point au or um matera ire rout er the eir- The current flows from armature contact nnger 43 through `the amature 20, field coil 21, brake e011 22 to resistor bank F, through the resistors to top contact 30F and then through contacts of group 1 to the top contact finger 44 and through connection 45 to L2. On succeeding steps the current passes from bankF to contacts lc-d-e and f of group -1 at the adjacent points leaving the successive divisions of the resistor bankF `out of the circuit until on the, last point all are left out. The contacts v2A and B of group 2 make the connections contacting with fingers 46 and 47 to close the shunt circuit for the armature shunt. vIi' this feature is not desired, these contacts are simply omitted and the number of speeds in hoisting `will be reduced by two. If these contacts are used as shown, on the first point the current divides at the contacts of group 3, part flowing from the contact finger next to the bottom one, through the end division of resistor bank A, through the wire 61 to the connected contact finger 47, through the contacts 2A and B to the contact finger 46 connecting with the point between the armature and the field. 0n the second point the current divides at the third contact finger from the bottom, partfiowing through the two division of the resistors, through wire 61, thence as before.

With the controller on the lowering side, the current will iiow from L1, wire through the blowout coil 31 and wire 41 and connected contact finger 42A, through the contacts 5A and 5B of group 5 to finger 46 and connection point' between the armature 20 and fleldf21. The current here divides part fiowing through the field 21 and brake 22 and all of the resistor bank F to the second contact linger from the top, through the contacts 4A and 4C of group 4, the top contact finger 44 and wire 45 to L2; the other part of the current passes through the armature and all of bank A, through wire 61 and its connected contact finger 47 to contact 4B of group 4 to the top contact finger, thence through wire to L2. The movable bridge is formed by the contacts of group 7, the contacts 7A-B-C DE plus the contacts 7F-G-H constituting the bridge 25 indicated in Fig. 1. The connection S between the two resistor banks is constituted by the contacts 4A4B. From the iirst to the fourth pointsthe contacts of this group engage successive points of division of resistor bank A with successive points of division of bank F through contacts 7A, 7B, 7C, 7D, 7E, 7F, '7G and'lH and connecting wire 71; from the fifth point on to the last, this bridge connection is open. From the sixth point on to the last the L2 side of the line is not connected to the contacts of group 4 but instead is connected by the bottom contact finger to the eeutaetu of group s. `,on the sixth peint the nem 13? current passes through resistor bank F-to the second contact finger from the top, contacts of group 4, the contact i'lnger 47 and connected wire 61, the end division of bank A, the second contact finger from the bottom,` contacts of group 6 Yto the bottom contact finger to line L2. On each of the remaining steps an additional division oi' resistor bank A is added to the field path. At the same time the resistance of the armature path on each or the steps o, 'r and a is reduced one division. 145

On the sixth step the armature current flows through all of resistor bank A, except the last division, to the second contact finger from the bottom, contacts of group 6 to bottom contact finger to L2. On the eighth step only one diviaan of bmx A 1s left m the armature circuit, the current passing from the fourth contact ringer from the bottomV to the contacts o! group 6,

thence to L2 as'before. At the off-point, the safety dynamic braking circuit is completed by two of the contacts of group '1, connecting the field, armature and theilrst division of bank A is a closed circuit. y f

Fig. 4 shows only one arrangement of the stationary contact fingers or brushes and contacts on thel drum that may be used with this system. Other groupings of contacts vmight be preferred to make simpler castings for the drum parts. I do not wish to limit my invention to Ie. particular type of controller construction,'but tocover the location and interconnections o! the motor, brake and resistors in a system of control .as shown principally in Fig'. 1, 'so that 4all of. the resistors are in .use all of the time in lowering.

, Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the mechanism herein, disclosed, provided the means stated by any of the `following claims or the equivalent of such stated means be employed.

I therefore particularly point out and distinctly'claim as my inventionz 1. In an 'electric control system for motors of the type comprising an amature and series iield winding. a circuit including a loop comprising the field winding and a first resistor bank the-armature and a accord resistor bank, a bridge connection across `said two resistor banks, including all oi' the resistance inthe loop, a-bridge connection movable' with respect to both resistor banks substantially throughout the length thereof to vary the amount of Veach included in the loop, a power line connected to said loop between said eld winding and armature and a second power line movably connected vto said second resistor to transfer resistance from the amature path to the meld winding path and vice versa between said power lines. y

2. In an electric control system4 tor motors of the typecomprising an armature and series field winding,.means for connecting the yiield winding and a resistor in one path and the amature and a second resistor in a parallel path-to form a closed loop, a movable bridgeconnected to the two resistors and forming a loop of variable resistance containing the motor Varmature and eld winding, a power line connected to a point between the neld winding and armature in said loop and the other power line being movably connected to said second resistor, and adapted to transfer portions of said resistors i'romone oi' said pathsto the other to vary the voltage on the armature and to vary the I leld strength.

3. In an electric control system for motors oi' i the type comprising an armature and series ileld winding, means for connecting the neld winding and a resistor bank in one path and the .armature and a'. second resistor bank in a parallel path, a connection between the two resistors for including variable amounts thereof in an internal loop containing the armature-and eld winding,

.a power line connected between said field windsustain means for connectingthe neld winding, the armature, and resistors in a, closed loop, a movabler bridge connection between points on said loop resistors for varying the resistance in said closed loop; and power-connections to the closed loop, one power line being connected between the armature and the ileld winding and the other being movably connected to the resistors, the movable connection of said power line being adjustable to shift portions oi' the resistors from the armature p'ath to the ileld winding path and vice versa to give varying voltage on the armature and varying ileld strength.

.5.'In a system oi' control for hoist motors of the class comprising a ileld winding andan armature, and requiring power or dynamic braking, means for providing a duplex circuit, comprising connecting the rleld winding and a resistor, and the armature anda second resistor in a vclosed loop with one terminal of the ileld connected to one terminal of the armature and a connection between the said two resistors movable with respect to both providing a dynamic braking circuit of varying resistance, and power connections to the closed loop, one power line being connected to a point between the eld winding and the armature, and the other being movably connected to the second resistor to vary respectively the resistance of the armature and neld winding paths and thereby to vary the voltgdon the armature and, the strength o! the 6. In a control system for hoists, motors of the type having an armature and ileld winding, a closed circuit including the armature and field winding of the motor and resistors, a power line connected to said 'closed circuit placing said armature and eld winding in parallel paths, a

.variable connection between points on said resistors forming a dynamic braking loop including the armature and eld winding and for varying the amount of said resistors in said dynamic breaking loop, while maintaining all 'of said resistors in said closed circuit for any and all operating speeds controlled by the system and another power line variably connected to said resistors to shift the same between the amature and neld winding paths to vary'the armature voltage and neldstrength.

7. In a control system for hoists in which a series motor is driven as a generator during lowering to retard overhauling loads, means for obtaining the maximum dissipation of the energy stored in the load tobe loweredwith a minimum provision of resistor elements, comprising a closed circuit including the armature and field winding of the motor and resistors, means for forming a dynamic braking loop including said ileld winding and amature, and for varying the amount of said resistors in said loop, means for shifting resistors between the armature and eld winding paths to vary the armature voltage and the field strength, a power line connected between said armaturev and said eld winding and another power line movably connected to said resistors, all of said resistors being utilized for the dissipation -of energy at any and all loperating positions of said system.

8. In an electric hoist system and apparatus', a pair of power supply mains, a motor comprising an armature and series ileld winding. and means including circuit controlling means for selectively establishing: a hoist holding circuit comprising a ilrst closed loop containing, in series relation, the

los

armature, the series ileld winding and loop resistance; then establishing a lowering circuit comprising a second closed loop containing, in serial relation, the armature, the series field winding, and second loop resistance in two parts, one part being at least a. portion of the said ilrst loop resistance, and the circuit comprising a series resistance connected at one portion to the loop at a point between the two parts of the said second loop resistance, and connected at another portion to one of the power lines, the other power line being connected to the loop at a point between the series eld winding and amature, thus providing resistance in series respectively with the armature and eld winding across the line through the series resistance; and then establishing another lowering circuit comprising a third closed loop containing, in serial relation, the armature, the

series ileld winding and third loop resistance in two parts, a rst part o! the resistance being the said series resistance, and a second part being at least a part oi said rst loop resistance, one power line being connected to a point between the ilrst and second parts of the said third loop resistance, the other power line being connected to a point between the series tleld winding and armature, thus providing resistance in series respectively with the armature and eld winding across the line, which is respectively less and greater than in the first mentioned lowering circuit.

9. The method of controlling a hoist motor comprising an armature and series ileld winding, in association with a pair of power mains, resistor means and controller means for establishing electric circuits including resistance oi the resistor means and for varying the resistance thereof in the circuits, which includes connecting the armature and ileld winding and resistor means having a rst ohmic value in a nrst closed loop to oppose lowering; then connecting the armature, series field winding and resistor means having a second ohmic value in a second closed loop, and connecting resistor means in series with the second loop at an intermediate point of the resistor means having the said second ohmic value, and connecting one power line to the second loop at a point between the armature and field winding and the other power line to the series resistor means, with the field winding and armature respectively across the line through the series resistor means each in series with a part of the second resistor means, to effect lowering at one speed; then connecting the armatureand neld winding and resistor means having a third ohmic value in a third closed loop, and connecting one power line to the third loop at a point between the field winding and armature, and the other power line to the third loop at an intermediate part of the resistor means having the third ohmic value, with the eld winding and armature respectively across the line each in series with a part of the third resistor means, the part in series with the field winding and armature respectively being of greater and lesser ohmic value than in the second closed loop, to effect lowering at a second speed.

`.mams F. scHNABEL. 

